In the mass production of semiconductor products, optical photolithographic systems are typically used to pattern layers of material that form the semiconductor devices. State of the art photolithographic systems, as used in the mass production of semiconductor products, generally have a resolution capability of no less than 0.5 micron.
A known method for resolving pattern line features having a minimum dimension of less than 0.5 micron by using conventional photolithography is achieved by use of a "spacer sidewall deposition" or a "spacer". The spacer method uses conventional photolithography to position a pattern line feature in a first layer of a material which overlies a layer of a semiconductor device to be etched. Subsequently, a conformal material is deposited to overlie the patterned first layer and is anisotropically etched to leave a remnant of the conformal material, known as the spacer, which is integral with and situated along the edges of the pattern line feature in the first layer. If the material of the line feature is selectively etched with respect to the spacer material, a pattern of spacers is formed on the layer or the semiconductor device to be etched. The spacer feature has a minimum dimension in the submicron range of 0.05 to 0.5 micron depending upon the original thickness of the conformal layer. In this manner, a spacer can function as a secondary etching mask for the layer of the semiconductor device to be etched. The pattern of spacers, overlying the layer of the semiconductor device to be etched, is etched anisotropically with an etch process that selectively etches the layer of the semiconductor device rather than the spacers. The resulting pattern lines which are a positive image of the pattern of spacers are etched into the first layer of material and have a much greater resolution than that which could be formed by conventional photolithographic systems. The aforementioned method has many applications for the patterning of submicron lines in the production of semiconductor products. Moreover, in addition to the patterning of submicron lines, there are also many applications in the semiconductor industry, such as in the manufacture of bipolar devices, for the patterning of submicron openings. Unfortunately, conventional photolithography does not have sufficient resolution capability to pattern submicron lines or openings.
A method for forming a submicron trench is taught by Antonio Alvarez in U.S. Pat. No. 4,735,681 entitled "Fabrication Method For Sub-Micron Trench" and assigned to the assignee hereof. Spacer material is used to form a hole in a masking layer which is subsequently transferred into an underlying substrate.